1. Field of the Invention
The present invention relates to a tool especially adapted for use in fastening together sections of heating and air conditioning ducts.
2. Description of the Prior Art
Conventional heating and air conditioning ducts in residential, commercial and industrial buildings are assembled from a number of separate duct sections which are manufactured in lengths small enough to be transported to a job site. The duct sections are formed of galvanized, cold-rolled sheet steel, typically of 18 or 20 guage thickness. The duct sections are manufactured in the shape of hollow, rectangular prisms, open at both ends and having flanges which extend transversely outward a short distance at the open ends perpendicular to the sides of the duct sections. The peripheral edges of the flanges are bent back to a disposition parallel to the sides of the duct sections from which the flanges transversely project. The peripheral edges of the flanges thereby define lips which extend a short distance perpendicular to the flanges from which they are formed and parallel to the sides of the duct sections from which the flanges transversely project. Each of the lips is formed of a fold of metal to double the effective thickness of the lip so as to provide additional reinforcement.
In cross section, the flanges and lips form a generally "L-shaped" configuration with the side of the duct from which they project at the open end of the duct section. The sides, flanges, and lips of each duct section are all formed from a single, unitary sheet of cold-rolled metal. Due to this manner of fabrication, the flanges and lips do not extend around the corners of the duct sections, but terminate at right angles relative to the corresponding flanges and lips that project from adjacent sides of the duct sections.
Angle shaped corner fasteners, manufactured of cold-rolled sheet steel and punched with apertures adapted to receive fasteners, such as bolts, are used as the primary means of connecting adjacent duct sections together. The corner angle fasteners each have a pair of legs intersecting at right angles. The two perpendicular legs of a corner angle are seated upon the surfaces of the adjacent mutually perpendicular flanges projecting from adjacent sides of a duct section. Four corner angle fasteners are seated on the flanges at each end of a duct section for coupling to another duct section. Similarly, the legs of four other corner angle fasteners are seated flush upon the flanges projecting from adjacent sides of another duct section to be joined to the first duct section. Bolts are then passed through each pair of facing corner angle fasteners, thereby compressing the flanges at the abutting ends of the duct sections therebetween. The juxtaposed faces of the flanges are previously coated with an adhesive sealant to prevent the leakage of air at the duct section interface.
For ducts of large cross section it is necessary to provide intermediate clamps to compress the interior portions of juxtaposed flanges together between the corner angles. These clamps are generally C-shaped in cross section and capture the lips of juxtaposed flanges therebetween.
In present practice in the installation of heating and air conditioning ductwork, the assembly together of duct sections is an arduous, laborious and time comsuming process. The corner angle fasteners are of a size designed to nest snugly in contact with the flanges and are designed to be confined between the walls of the sides of the duct sections and the lips protruding from the flanges. Indeed, the breadth of the flanges is such, that according to conventional practice, they must be pounded into place to seat in contact against the flanges using a steel hammer or mallet. Furthermore, to hold the corner angle fasteners in place, it is conventional practice to use a steel hammer or mallet to turn over the ends of the lips projecting from the flanges at the terminal ends of the flanges to thereby entrap the corner angles against the flanges. Also, it is conventional practice to deform the clamps that are located intermediately between the corner angle fasteners to firmly compress the intermediate portions of the flanges together using a steel hammer or mallet.
A steel hammer or mallet has heretofore been used as the primary tool in the assembly of heating and air conditioning duct sections. Age-old tools of this type have been available and have, for many centuries, been used to deform and work metal into a desired shape. However, as previously noted, the assembly of heating and air conditioning duct sections together using such a general purpose tool is extremely arduous and time consuming.
Using a conventional hammer or mallet a time of from approximately 8 to 12 minutes is required to fasten the facing four corner sections of two duct sections together. Competent tradesmen who perform such work, like others in the construction industry, are typically paid on an hourly basis and the expenses for labor in installing heating and air conditioning ducts are very significant. Duct sections may vary in lengths from less than two feet to greater than eight feet, and even a relatively small installation involves the coupling together many duct sections. The time involved in coupling duct sections together is further lengthened where the ducts include a number of branches and turns, since relatively short duct sections and multiple couplings are required in such instances. Each coupling interface requires approximately the same time for completion, regardless of the length of the duct sections involved.
A further disadvantage of the use of conventional hammers and mallets to couple together duct sections is that the operation is extremely noisy. Additional heating and air conditioning ductwork is often installed in existing buildings where commercial and industrial operations are taking place only a short distance from the areas of new duct installation. Although it is frequently not difficult to physically separate the areas of construction from the operating office and commercial space so as to prevent disruption of continuing business and manufacturing operations, the noise produced by hammering the duct flanges, corner angle fasteners and clamps permeates the entire surrounding area and is frequently so disruptive as to bring day-to-day business operations to a standstill.